The luminescent bodies of organic electroluminescent devices (hereinafter may be referred to as “organic EL devices”) can be formed in a planar shape, and the color of light generated therefrom can be white or a color close to white. Therefore, such organic electroluminescent devices can be used as light sources of lighting devices or in applications of backlight units for display devices.
White organic EL devices are produced as organic EL devices used in lighting applications. Many of such white devices are called the stacked or tandem type in which luminescent layers that generate complementary colors are stacked. The stacks of such luminescent layers are mainly stacks of yellow-blue layers or green-blue-red layers.
However, the efficiency of currently known white organic EL devices is not high enough for lighting applications described above. Therefore, in order to use such organic EL devices in these applications, their light extraction efficiency must be improved.
In order to improve the light extraction efficiency of organic EL devices, it is known to provide various structures on their light-extraction substrates. For example, in one proposal, prisms containing a fluorescent compound are provided on a light emitting surface (Patent Document 1: Japanese Patent Application Laid-Open No. 2002-237381). In another proposal, a micro-lens array is provided on a light emitting surface (Patent Document 2: Japanese Patent Application Laid-Open No. 2003-59641). With these structures, light can be preferably gathered, and the efficiency is thereby improved.
However, in the above-described lighting organic EL devices of the stacked type, the depths from the light emitting surface to the luminescent layers are different for different luminescent layers generating different colors. Therefore, when the above structures are used in such organic EL devices, there occurs a problem in that the color tone when the light emitting surface is viewed from a front direction is significantly different from the color tone when the light emitting surface is viewed at an oblique angle with respect to the front direction.